Semiconductor Chip Passivation Structures and Methods of Making the Same

ABSTRACT

Various semiconductor chip passivation structures and methods of making the same are disclosed. In one aspect, a method of manufacturing is provided that includes applying a polymeric passivation layer to a side of a semiconductor chip. The side of the semiconductor chip includes plural conductor pads. Plural openings are formed in the polymeric passivation layer to expose the plural conductor pads. Plural conductor structures are formed on the plural conductor pads.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to semiconductor processing, and moreparticularly to semiconductor chip passivation structures and methods ofmaking the same.

2. Description of the Related Art

A conventional semiconductor chip destined for flip-chip mounting to aprinted circuit board or semiconductor package substrate will typicallyconsist of two principle sides: one side provided with a plurality ofinput/output conductors, and an opposite side that may or may not befitted with a heat spreader. This general configuration holds truewhether the chip is implemented as a bulk silicon or semiconductordevice or a semiconductor-on-insulator device. The principle side of thesemiconductor chip that is provided with the input/output conductor padstypically includes one or more metallization layers that are formedabove the active device portion of the chip and an array of conductorpads connected to the metallization layers by vias. The top-mostmetallization layer includes the array of conductor pads and issometimes referred to as a redistribution layer. The conductors pads areprovided with under bump metallization (UBM) structures suitable toprovide metal diffusion resistant surfaces for solder bump placement.

In a C4 flip-chip interconnect process, a plurality of solder bumps areapplied to the bump pads and a corresponding plurality of solder bumpsare formed on respective conductor pads on a package substrate orprinted circuit board. The respective collections of bumps are broughttogether and a reflow process is performed in order to establish aplurality of solder joints between the semiconductor chip and theprinted circuit board or package substrate. It is important to protectthe top-most metallization layer from contamination and physical damageprior to bumping and assembly with a substrate. A damaged orcontaminated bump pad might lead to device failure. In a conventionalprocess, this protective function is provided by a passivation structurethat is applied to the side of the semiconductor chip that includes thebump pads. The passivation structure undergoes a masking and etchprocess to expose the conductor pads. A polyimide layer is often appliedover the passivation layer, including over the previously etchedopenings to the conductor pads, to provide protection fromthermomechanical stresses that might otherwise damage chip structures.Thereafter, the polyimide layer is lithographically processed toessentially reestablish openings leading to the underlying bump pads,and then metal deposition processes and solder application processes areused in order to establish the under bump metallization and solderbumps.

In one conventional process, a passivation structure consists of a sixlayer stack of alternating layers of silicon nitride and undopedsilicate glass. Processing at this stage is done at the wafer level, soapplication of each of the silicon nitride and undoped silicate glasslayers requires the wafer to be moved in and out of a chemical vapordeposition (CVD) chamber and subjected to CVD in order to establish agiven layer. Consequently, a dozen or more material movements and stepswill be required in order to establish a conventional six layerpassivation stack as well as the six deposition processes themselves.The number of both material handling and CVD processes represents aninvestment of manufacturing time and materials.

In some conventional processes, the steps of passivation structureformation and polyimide layer application are divided between different,and often geographically separated, manufacturing facilities. Forexample, it is not uncommon for one vendor to manufacture thesemiconductor chip up to and including the passivation structure. Atthis point, the wafer is shipped to a bumping vendor that applies thepolyimide layer and then performs the subsequent lithographic processingto form the UBM structures and solder bumps. Thus, the passivationstructure is formed by one vendor and the polyimide and under bumpmetallization are formed subsequently by another vendor.

The present invention is directed to improving upon the aforementionedconventional techniques.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method ofmanufacturing is provided that includes applying a polymeric passivationlayer to a side of a semiconductor chip. The side of the semiconductorchip includes plural conductor pads. Plural openings are formed in thepolymeric passivation layer to expose the plural conductor pads. Pluralconductor structures are formed on the plural conductor pads.

In accordance with another aspect of the present invention, a method ofmanufacturing is provided that includes forming plural conductor pads ona side of a semiconductor chip and applying a polymeric passivationlayer to the side of a semiconductor chip to cover the plural conductorpads. Plural openings are formed in the polymeric passivation layer toexpose the plural conductor pads. The side of the semiconductor chip iscoupled to a printed circuit. Plural electrical interconnects areestablished between the semiconductor chip and the printed circuitboard.

In accordance with another aspect of the present invention, an apparatusis provided that includes a semiconductor chip that has a side thatincludes plural conductor pads. A polymeric passivation layer is coupledto the side of the semiconductor chip. The polymeric passivation layerhas plural openings to the plural conductor pads. Plural conductorstructures are coupled to the side of the semiconductor chip. Each ofthe plural conductor structures has a portion positioned in one of theplural openings and coupled to one of the conductor pads.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the invention will become apparentupon reading the following detailed description and upon reference tothe drawings in which:

FIG. 1 is a sectional view of a small portion of an exemplaryconventional semiconductor chip package;

FIG. 2 is a portion of FIG. 1 shown at greater magnification;

FIG. 3 is a sectional view of a small portion of an exemplary embodimentof a semiconductor chip package;

FIG. 4 is a portion of FIG. 3 shown at greater magnification;

FIG. 5 is a sectional view of a small portion of an alternate exemplaryembodiment of a semiconductor chip package;

FIG. 6 is a portion of FIG. 5 shown at greater magnification; and

FIG. 7 is an exploded pictorial depicting some possible mounting schemesfor any of the package embodiments disclosed herein.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

In the drawings described below, reference numerals are generallyrepeated where identical elements appear in more than one figure.Turning now to the drawings, and in particular to FIG. 1, therein isshown a sectional view of a small portion of an exemplary conventionalsemiconductor chip package 10 that includes a package substrate 15 uponwhich a semiconductor chip or die 20 is flip-chip mounted. The substrate15 is composed of a series of polymer layers built up and interspersedwith conductor traces and vias that are not visible. The substrate 15includes a plurality of conductor pads, one of which is shown andlabeled 25. The conductor pad(s) 25 may be interconnected to theaforementioned vias and traces. A typical conventional substrate 15includes scores or hundreds of such conductor pads 25.

A passivation structure 30 is formed on a surface 35 of thesemiconductor chip 20 and, as described in more detail below, consistsof a laminate of several alternating layers of dielectric material. Apolyimide layer 40 is formed on the passivation structure 30. Openingsare formed in the polyimide layer 40 and the passivation structure 35 at45 and 50, respectively, so that an under bump metallization (UBM)structure 55 may be formed with a bonding surface 60 that extendslaterally on the polyimide layer 40 and another bonding surface 65 thatextends to and metallurgically bonds with a conductor or bump pad 70 ofthe semiconductor chip 20. The bump pad 70 may be one of scores orhundreds of such bump pads that are formed on or near the surface 35 ofthe semiconductor chip 20. There may be plural interconnect structuresthat connect to the bump pad 70 and other similar bump pads that are notvisible. One of the interconnect structures is shown connected to thebump pad 70 and labeled 73. The different cross-hatchings of theinterconnect structure 73 a and the bump pad 70 implies that the twostructures are physically distinct, but connected structures. However,it should be understood that the bump pad 70 and the interconnectstructure 73 may be contiguous. A conductive metallurgical connectionbetween the pad 25 of the package substrate 15 and the UBM 55 of thesemiconductor chip 20 is established by way of a solder joint 75 thatconsists of corresponding portions of solder coupled to the UBM 55 andthe pad 25 that are merged metallurgically during a reflow process.

An underfill material layer 80 is interposed between the polyimide layer40 and the package substrate 15 in order to help alleviate differentialstresses associated with differences in coefficient of thermal expansionbetween the substrate 15 and the semiconductor chip 20. The underfill 80is typically composed of an epoxy with or without some form offiberglass fill material.

The passivation structure 30 is designed to protect the top-mostmetallization, as exemplified by the bump pad 70 and the interconnectstructure 73 shown in FIG. 1, prior to bumping. In a typicalconventional process, the bumping process entails forming the opening inthe passivation structure 30 at 50 by appropriate masking and etching,applying the polyimide layer 40, forming the opening in the polyimidelayer 40 by appropriate masking and etching, and metal deposition andetch definition to define the UBM 55, and application of a portion ofsolder to the UBM 55 that will eventually form a substantial fraction ofthe solder joint 75. The polyimide layer 40 is designed to protect thesemiconductor chip 20 from thermal mechanical stresses that will ariseafter flip-chip mounting to the substrate 15 as shown in FIG. 1. Theportion of the package 10 circumscribed by the dashed oval 85 will beshown at greater magnification in FIG. 2 to facilitate the descriptionof further details of the conventional passivation structure 30.

Attention is now turned to FIG. 2. As is evident, the passivationstructure 30 formed between the semiconductor chip 20 and the polyimidelayer 40 consists of a stack of six layers 90, 95, 100, 105, 110 and115. The layers 90, 100 and 110 consists of undoped silicate glass (USG)and the layers 95, 105 and 115 consist of silicon nitride. The siliconnitride and USG layers are alternatively applied in separate depositionprocesses that typically consist of a chemical vapor deposition (CVD)process for each. The drawback with the conventional passivationstructure 30 is that with such a large number of individual layers 90,95, 100, 105, 110 and 115, there is a penalty in terms of processingtime and complexity in order to yield the passivation structure 30. Eachof the layers 90, 95, 100, 105, 110 and 115 will typically requiremovement of a semiconductor workpiece or wafer into and out of adifferent CVD chamber with an attendant time associated with bothworkpiece movement and processing.

Attention is now turned to FIG. 3, which is a sectional view of a smallportion of an exemplary embodiment of a semiconductor chip package 120that includes a package substrate 125 upon which a semiconductor chip130 is flip-chip mounted. The package 120 may be lidless as depicted orfitted with any type of lid or heat spreader (not shown) as desired. Thesubstrate 125 may consist of a core/build-up configuration. In thisregard, the substrate 125 may consist of a central core upon which oneor more build-up layers are formed and below which an additional one ormore build-up layers are formed. The core itself may consist of a stackof one or more layers. One example of such an arrangement may be termeda so called “2-4-2” arrangement where a four-layer core laminatedbetween two sets of two build-up layers. The number of layers in thesubstrate 125 can vary from four to sixteen or more, although less thanfour may be used. So-called “coreless” designs may be used as well. Thelayers of the substrate 125 consist of an insulating material, such asvarious well-known epoxies, interspersed with metal interconnects.Optionally, the substrate 125 may be composed of well-known ceramics orother materials suitable for package substrate or printed circuitboards. To provide for electrical connectivity, the substrate 125 isprovided with a plurality of conductor pads, one of which is shown andlabeled 135, and that may be connected to other interconnect structureswithin the body of the substrate 125 that are not visible.

The semiconductor chip 130 may be any of a myriad of different types ofcircuit devices used in electronics, such as, for example,microprocessors, graphics processors, combined microprocessor/graphicsprocessors, application specific integrated circuits, memory devices orthe like, and may be single or multi-core or even stacked withadditional dice. To provide electrical connectivity with externaldevices, the semiconductor chip 130 may be provided with a plurality ofinput/output structures or conductor pads, one of which is shown andlabeled 140, that provide interconnects to various conductor structureswithin the semiconductor chip 130 that are not visible. The conductorpad(s) 140 may be formed using well-known lithographic patterning andmetal deposition and/or plating techniques.

In lieu of the laminate passivation structure 30 depicted in FIGS. 1 and2, a polymeric passivation layer 145 may be applied to a side 147 of thesemiconductor chip 130. In this illustrative embodiment, the polymericpassivation layer 145 may be monolithic and provide both a passivationfunction and a thermal mechanical stress protection function that wouldotherwise provided by the separate passivation structure 30 and thepolyimide layer 40 in the conventional embodiment depicted in FIGS. 1and 2. An opening is provided in the polymeric passivation layer 145 at150 in order to provide access to the underlying conductor pad 140 for aportion 155 of a UBM layer 160. A bonding surface 165 of the UBM layer160 projects over a portion of a surface 170 of the polymericpassivation layer 145. A variety of materials may be used for the UBMlayer 160, such as copper, gold, silver, platinum, nickel, vanadium,aluminum, combinations of these or the like. In an exemplary embodiment,the UBM layer 160 may consist of a titanium layer on the bond pad 140, anickel-vanadium layer on the titanium layer and a copper layer on thenickel-vanadium layer. The copper layer is designed to readily wetsolder. A solder joint 175 is provided between the UBM structure 160 andthe conductor pad 135 of the package substrate 125. The solder joint 175may be composed of lead-based or lead-free solder as desired. Exemplarysolders include tin-lead (63% Pb 37% Sn), tin-silver (about 97.3% Sn2.7% Ag), tin-copper (about 99% Sn 1% Cu), tin-silver-copper (about96.5% Sn 3% Ag 0.5% Cu) or the like. In an exemplary embodiment, thesolder structure 175 consists of a reflowed combination of eutectictin-lead solder composition (63% Pb 37% Sn) nearer the package substratepad 150 and a higher lead content (97% Pb 3% Sn) portion proximate theUBM structure 160. Prior to mounting the semiconductor chip 130 on thesubstrate 125, a portion of high lead content solder may be fashionedinto a bump on the conductor pad 140, and a bump of eutectic tin-leadsolder may be formed on the conductor pad 135 of the substrate, bothusing well-known solder stenciling techniques. The two bumps maythereafter be joined in a reflow process to establish the joint 175. Anunderfill material 178 may be deposited between the substrate 125 andthe semiconductor chip 130 to lessen the effects of differential CTEbetween the semiconductor chip 130 and the substrate 125. The underfillmaterial 178 may be, for example, an epoxy resin mixed with silicafillers and phenol resins, and deposited using well-known capillaryinjection or other techniques.

A small portion of the package 120 is circumscribed by the dashed oval180. The dashed oval 180 will be shown at much greater magnification inFIG. 4. Attention is now turned to FIG. 4. Note that a small portion ofthe semiconductor chip 130, a small portion of the under fill materiallayer 178 and the polymeric passivation layer 145 are visible in FIG. 4.As noted above, the polymeric passivation layer 145 may be applied tothe surface 147 of the semiconductor chip 130 as a monolithic layer in asingle deposition process if desired. Of course, the semiconductor chip130 will not be coupled to the package substrate 125, and may be rotatedby as much as 180° from the orientation depicted in FIG. 4, at the timethe polymeric passivation layer 145 is applied. In an exemplaryembodiment, the polymeric passivation layer 145 may consist ofpolyimide. Optionally, the polymeric passivation layer 145 may becomposed of benzocyclobutene or like polymers, or other insulatingmaterials such as silicon nitride or the like. Spin coating, CVD orother deposition processes may be used. If polyimide is selected, aheating step may be performed to cure the polymeric passivation layer145. An appropriate thickness for the polymeric passivation layer 145will depend on overall device size and geometry. In an exemplaryembodiment, the polymeric passivation layer 145 may have a post-curethickness of about 4.0 to 7.0 μm. Thus, the polymeric passivation layer145 can be deposited in a single relatively straightforward processingstep to yield a layer that serves both as passivation and as thermalmechanical cushioning and thus eliminates the need for the six separatedeposition steps and dual etches that would be required to establish themulti-layer laminate passivation structure 30 depicted in FIGS. 1 and 2and described elsewhere herein.

An appropriate opening in the polymeric passivation layer 145 is made at150 to expose the conductor pad 140 using well-known lithographicpatterning or other material removal techniques. Thereafter, the UBMlayer 160 may be formed using CVD, physical vapor deposition or othermaterial deposition techniques. The UBM 160 may be applied en masse onthe semiconductor chip 130 and thereafter patterned lithographically.

An alternate exemplary embodiment of a semiconductor chip package 120′may be understood by referring now to FIG. 5, which is a sectional viewlike FIG. 3. In this illustrative embodiment, the package 120′ mayconsist of the substrate 125, the semiconductor chip 130 mounted thereonas well as the conductor pad 135, the conductor pad 140, the UBM 160,the solder joint 175 and the underfill 178 all as generally describedelsewhere herein. However, in this embodiment a passivation structure190 may be formed on the semiconductor chip 130 and a polymericpassivation layer 145′ may be formed on the passivation layer 190. Toestablish the UBM 160, openings may be formed in the polymeric layer145′ and the passivation layer 190 at 195 and 200 respectively usingwell-known lithographic patterning or other material removal techniques.A small portion of the package 120′ is circumscribed by a dashed oval205. The dashed oval 205 will be shown at greater magnification in FIG.6.

Attention is now turned to FIG. 6, which as just noted, is the portion205 of FIG. 5 shown at greater magnification. Note that a small portionof the semiconductor chip 130, a small portion of the under fill 178 andthe films 190 and 145′ are visible. Providing the passivation layer 190between the polymeric passivation layer 145′ and the underfill 178 maybe useful in circumstances where the semiconductor chip 130 may be partof some larger workpiece such as a wafer that is processed up to thepoint where the conductor pad 140 depicted in FIG. 5 is ready to receivea UBM structure but such processing is destined to take place at anotherfacility. In this way, the passivation layer 190 may be applied toprotect the underlying conductor pad 140 during material movement toanother location. At this point, the polymeric passivation layer 145′may be applied as a monolithic layer as shown and then the openings at195 and 200 shown in FIG. 5 may be made in order to allow the UBMstructure 160 to be formed. It should be understood however that thepassivation layer 190 may need not be a single layer but perhaps one ora small number of layers that are much less than the six layer laminate30 depicted in FIGS. 1 and 2. In this way, a savings in terms of bothmaterial and time may be realized while still providing for an interimconductor pad protection prior to the application of the polymericpassivation layer 145′.

Attention is now turned to FIG. 7, which is an exploded pictorialdepicting some possible mounting schemes for any of the packageembodiments disclosed herein. In this regard, the package embodiment 120is shown exploded from another circuit board 210, which may be amotherboard, a daughterboard, or virtually any kind of circuit board towhich the package 120 may be mounted. The package 120 includes theaforementioned semiconductor chip 130, which is shown bump side up andincludes an array of solder bumps 215 that will join metallurgically toa corresponding array 217 of solder bumps on the package substrate 125to establish a plurality of solder joints to connect the semiconductorchip 130 and the package substrate 125. Thus, to achieve the mountingshown in FIG. 3, the semiconductor chip 130 is flipped over as indicatedby the arrow 220 and flip-chip mounted on the package substrate 125 byway of reflow process. It should be understood that the semiconductorchip 120 may be coupled not only to a package substrate, but tovirtually any type of circuit board. The circuit board 210 may be, inturn, mounted to another electronic device 225, which may be a computer,a digital television, a handheld mobile device, a personal computer, aserver, a memory device, an add-in board such as a graphics card, or anyother computing device employing semiconductors.

Any of the exemplary embodiments disclosed herein may be embodied ininstructions disposed in a computer readable medium, such as, forexample, semiconductor, magnetic disk, optical disk or other storagemedium or as a computer data signal. The instructions or software may becapable of synthesizing and/or simulating the circuit structuresdisclosed herein. In an exemplary embodiment, an electronic designautomation program, such as Cadence APD, Encore or the like, may be usedto synthesize the disclosed circuit structures. The resulting code maybe used to fabricate the disclosed circuit structures.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A method of manufacturing, comprising: applying a polymericpassivation layer to a side of a semiconductor chip, the side includingplural conductor pads; forming plural openings in the polymericpassivation layer to expose the plural conductor pads; and formingplural conductor structures on the plural conductor pads.
 2. The methodof claim 1, wherein the applying a polymeric passivation layer comprisesapplying a monolithic layer.
 3. The method of claim 1, wherein theapplying a polymeric passivation layer comprises applying a layer ofpolyimide.
 4. The method of claim 1, wherein the forming pluralconductor structures comprises forming plural under bump metallizationstructures on the plural conductor pads.
 5. The method of claim 4,comprising forming plural solder structures on the plural under bumpmetallization structures.
 6. The method of claim 1, comprising attachingthe side of the semiconductor chip to a printed circuit board.
 7. Themethod of claim 6, comprising coupling the printed circuit board to anelectronic device.
 8. The method of claim 1, wherein the method isperformed by executing instructions stored in a computer readablemedium.
 9. A method of manufacturing, comprising: forming pluralconductor pads on a side of a semiconductor chip; applying a polymericpassivation layer to the side of a semiconductor chip to cover theplural conductor pads; forming plural openings in the polymericpassivation layer to expose the plural conductor pads; and coupling theside of the semiconductor chip to a printed circuit; and establishingplural electrical interconnects between the semiconductor chip and theprinted circuit board.
 10. The method of claim 9, wherein the applying apolymeric passivation layer comprises applying a monolithic layer. 11.The method of claim 9, wherein the applying a polymeric passivationlayer comprises applying a layer of polyimide.
 12. The method of claim9, wherein the forming plural conductor structures comprises formingplural under bump metallization structures on the plural conductor pads.13. The method of claim 4, wherein printed circuit board comprisesplural conductor pads, the establishing plural electrical interconnectscomprises forming plural solder joints between the plural under bumpmetallization structures and the plural conductor pads of the printedcircuit board.
 14. The method of claim 9, comprising coupling theprinted circuit board to an electronic device.
 15. An apparatus,comprising: a semiconductor chip having a side including pluralconductor pads; a polymeric passivation layer coupled to the side of thesemiconductor chip having plural openings to the plural conductor pads;and plural conductor structures coupled to the side of the semiconductorchip, each of the plural conductor structures having a portionpositioned in one of the plural openings and being coupled to one of theconductor pads.
 16. The apparatus of claim 15, wherein the polymericpassivation layer comprises a monolithic layer.
 17. The apparatus ofclaim 15, wherein the polymeric passivation layer comprises a layer ofpolyimide.
 18. The apparatus of claim 15, comprising a printed circuitboard coupled to the side of the semiconductor chip.
 19. The apparatusof claim 18, comprising an electronic device coupled to the printedcircuit board.
 20. The apparatus of claim 18, comprising pluralelectrical interconnects between the plural conductor pads of thesemiconductor chip and the printed circuit board.